US Vice President Kamala Harris is calling on all nations to respect and uphold the 2016 Permanent Court of Arbitration decision stating that expansive maritime claims by China over the South China Sea have no legal basis.

The Arbitral Tribunal ruling also determined that the area is part of the Philippines' exclusive economic zone and continental shelf.

Harris made the statement during a speech on Tuesday while she was on board BRP Teresa Magbanua in Palawan, the island province closest to the hotly contested South China Sea.

"I am here in Palawan to underscore the importance of our partnership in order to create economic opportunities, protect coastal ecosystems, maintain peace and stability, and uphold international rules and norms here in the South China Sea and around the world," Harris said.

"As the United States has long made clear: We support the 2016 ruling of the UN Arbitral Tribunal, which delivered a unanimous and final decision firmly rejecting China's expansive South China Sea maritime claims. The tribunal's decision is legally-binding, and must be respected," she added.

She also recognized the Philippine Coast Guard for being "on the frontlines of standing up for the international rules-based order."

"As you patrol these waters, you uphold the rules and norms that are vital to the prosperity of the Filipino people, and people around the world," she said, noting that their service also safeguards the lives and livelihoods of the people here.

Harris, the highest-ranking US official to visit Manila after President Ferdinand "Bongbong" Marcos Jr. assumed power, said the United States and the broader international community have a profound stake in the future of the region.

"We must stand up for principles such as respect for sovereignty and territorial integrity, unimpeded lawful commerce, the peaceful resolution of disputes, and the freedom of navigation and overflight in the South China Sea, and throughout the Indo-Pacific," she said.

"America's prosperity relies on the billions of dollars that flow through these waters every day. And we are proud to work with you in your mission," she added.

She reiterated that the United States would continue to stand with the Philippines "in the face of intimidation and coercion in the South China Sea."

In her first bilateral meeting with Marcos on Monday, Harris reaffirmed the American government's "unwavering" commitment to the Mutual Defense Treaty, emphasizing that the US would stand by the Philippines in the event of an attack in the South China Sea.

"Our relationship is based on mutual concerns about security for the region. We are both proud members of the Indo-Pacific. And in particular, as it relates to the Philippines, I will say that we must reiterate always that we stand with you in defense of international rules and norms as it relates to the South China Sea," Harris told Marcos.

"An armed attack on the Philippines armed forces, public vessels, or aircraft in the South China Sea would invoke US Mutual Defense commitments. And that is an unwavering commitment that we have to the Philippines," she stressed.

The MDT, the longest-running defense pact signed in 1951, seeks to boost the defense and security cooperation between the Philippine and US armed forces.